High Sensitivity Silicon Piezoresistor Force Sensor

ABSTRACT

Embodiments relate to systems and methods for sensing a force using a sense die. A sense die may comprise a chip comprising a slab; an actuation element configured to contact the slab at or near the center of the slab, and configured to apply a force to the slab; and one or more sense elements supported by the slab, wherein the ratio of the width of the slab to the distance between the one or more sense elements is at least 2/1. A method may comprise providing a sense die comprising a chip having a slab formed thereon; applying a force to the slab of the sense die; and determining the magnitude of the force applied to the slab via one or more sense elements attached to the slab, wherein the ratio of the width of the slab to the distance between the sense elements is greater than 2/1.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

In many industrial areas it is necessary to accurately measure themagnitude of a force. Force sensors can be used to measure a force or apressure. Various designs can be used and can rely on a displacement ofa component or a stress-field applied to a stress-sensitive element orcomponent to measure the presence of a force and/or an amount of theforce present on the sensor. Force sensors can experience forces abovetheir designed operating ranges (e.g., overforce situations), which canresult in damage to the force sensors.

SUMMARY

In an embodiment, a sense die may comprise a chip comprising a slab; oneor more sense elements supported by the slab, wherein the ratio of thewidth of the slab to the distance between the one or more sense elementsis at least 2/1; one or more bond pads supported by a first side of thechip, each of the one or more bond pads electrically coupled to at leastone of the one or more sense elements; a structural frame disposed onthe first side of the chip, wherein the structural frame is disposed atleast partially about the slab; and one or more electrical contactsextending through the structural frame, wherein the one or moreelectrical contacts are electrically coupled to the one or more bondpads.

In an embodiment, a method of sensing a force using a sense die maycomprise providing a sense die comprising a chip having a slab formedthereon; applying a force to the slab of the sense die; and determiningthe magnitude of the force applied to the slab via one or more senseelements attached to the slab, wherein the ratio of the width of theslab to the distance between the one or more sense elements is greaterthan approximately 2/1.

In an embodiment, a sense die may comprise a chip comprising a slab; anactuation element configured to contact the slab at or near the centerof the slab, and configured to apply a force to the slab; and one ormore sense elements supported by the slab, wherein the ratio of thewidth of the slab to the distance between the one or more sense elementsis greater than approximately 2/1, and wherein the distance between thesense elements is centered on the contact point between the actuationelement and the slab.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, referenceis now made to the following brief description, taken in connection withthe accompanying drawings and detailed description, wherein likereference numerals represent like parts.

FIG. 1 illustrates a schematic cross-section of a sense die according toan embodiment of the disclosure.

FIGS. 2A-2B illustrate another cross-section of a sense die according toan embodiment of the disclosure.

FIGS. 3A-3C illustrate a stress map of a surface of a sense dieaccording to an embodiment of the disclosure.

FIGS. 4A-4B illustrate the relationships between load on the sense die,location of the sense elements, and sensor output according to anembodiment of the disclosure.

FIG. 5 illustrates the relationship between contact radius and load onthe sense die according to an embodiment of the disclosure.

FIGS. 6A-6B illustrate cross sectional views of a sense die thatillustrate the relationship between contact radius and load on the sensedie according to an embodiment of the disclosure.

DETAILED DESCRIPTION

It should be understood at the outset that although illustrativeimplementations of one or more embodiments are illustrated below, thedisclosed systems and methods may be implemented using any number oftechniques, whether currently known or not yet in existence. Thedisclosure should in no way be limited to the illustrativeimplementations, drawings, and techniques illustrated below, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

The following brief definition of terms shall apply throughout theapplication:

The term “comprising” means including but not limited to, and should beinterpreted in the manner it is typically used in the patent context;

The phrases “in one embodiment,” “according to one embodiment,” and thelike generally mean that the particular feature, structure, orcharacteristic following the phrase may be included in at least oneembodiment of the present invention, and may be included in more thanone embodiment of the present invention (importantly, such phrases donot necessarily refer to the same embodiment);

If the specification describes something as “exemplary” or an “example,”it should be understood that refers to a non-exclusive example;

The terms “about” or “approximately” or the like, when used with anumber, may mean that specific number, or alternatively, a range inproximity to the specific number, as understood by persons of skill inthe art field; and

If the specification states a component or feature “may,” “can,”“could,” “should,” “would,” “preferably,” “possibly,” “typically,”“optionally,” “for example,” “often,” or “might” (or other suchlanguage) be included or have a characteristic, that particularcomponent or feature is not required to be included or to have thecharacteristic. Such component or feature may be optionally included insome embodiments, or it may be excluded.

Embodiments of the disclosure include systems and methods for improvingthe signal output from a sense die configured to detect force applied tothe sense die. Embodiments of the disclosure may comprise piezoresistiveelements unusually close to the center of the die, where theload-bearing actuation element makes contact to the die face. Throughstress mapping of the surface of the sense die, it was discovered thatthere is a small localized area of very high signal-generating stressnear the actuation element. When piezoresistive elements are implantedin this location, die sensitivities can be up to 100 times greater orhigher than traditional locations for the piezoresistive elements.Because the small areas of high stress constitute a localized contactphenomenon, no anisotropic etch is needed to form a diaphragm, andtherefore a “slab” die can be used. Using a slab die may have theadvantage of significantly higher proof loads (i.e. higher overloadprotection), while at the same time reducing cost because it is nolonger necessity to complete the anisotropic etch. Additionally, thismethod of positioning the piezoresistive elements may allow for asmaller die to be used, which may lower costs as well.

Typical uses of piezoresistive elements position the piezoresistiveelements at or near the center edge of a formed diaphragm. Typical forcesensors may use a stress field that is relatively distant from thecontact point between the actuation element and the sense die (or theload point). Embodiments of the disclosure may use a localized stressfield very near the load point. This localized stress field may be muchhigher in magnitude than the typically used distant stress field,leading to higher die output for a given load.

A technical benefit of the described method of positioning thepiezoresistive elements may include much higher die output for a givenload. Additionally, since a full wafer thickness may be used, nospecifically-defined diaphragm is required, and therefore the proof loadis significantly higher. Also, the costs of the sense die may be reducedbecause no etch steps are required to form a diaphragm, no speciallypatterned adhesive is required under the die (just a continuous layerrather than a “picture frame” pattern with an unsupported central area),and a smaller die can be used (costs are proportional to the size of adie, where even a 30% reduction is die side length may translates to acost reduction of up to 50%). The same general design and orientation ofthe piezoresistive elements may be similar to a traditional pressure orforce sensor, but the location of the piezoresistive elements may beadjusted.

FIG. 1 illustrates an embodiment of a typical sense die 100 according tosome embodiments that can be used to detect a force, including apressure. As shown, the sense die 100 can include a diaphragm or slab102, and a substrate 140 located near a first surface 103 of the sensor.The slab 102 may comprise one or more sense elements 120, 124 connectedto one or more electrical contacts 106. The sense elements 120, 124 maybe located on a second surface 105 of the slab 102. Optionally, asidewall 108 can be attached to a portion of a second surface 105 of thesensor. An actuation element 110 can be present within a cavity 112formed by the sidewall 108 and can serve to transfer a force to thesecond surface 105 of the slab 102. In some embodiments, the slab 102may comprise a solid slab. In some embodiments, the slab 102 may beattached to the substrate 140 via an adhesive 142.

The sense die 100 may be formed from silicon or other semiconductormaterial. While the sense die 100 is described with respect to beingformed from silicon, it should be understood that other materials canalso be used. In an embodiment, the sense die 100 can begin as a siliconchip and be processed to form the sense die 100, as described in moredetail herein. In some embodiments, the silicon chip may include arecess formed on the first surface 103 to form a diaphragm 102. Avariety of micro-fabrication techniques including, but not limited to,lithography techniques, wet etching techniques, and dry etchingtechniques may be used to form the recess. In some embodiments, thediaphragm 102 may be fabricated on the sense die 100 by back-sideetching of a silicon die (e.g., with a KOH etching technique, deepreactive ion etching, or other etching technique). However, it iscontemplated that any suitable process may be used, as desired. Thediaphragm 102 may have a height or thickness that is less than thethickness of the edges of the sense die 100, thereby forming thediaphragm 102.

The diaphragm or slab 102 is configured to flex in response (or at leasthave some elastic response) to an applied force, creating stress fieldsthat extend through the one or more sense elements 120 and 124, therebyallowing the applied force to be determined. In some embodiments, theelastic response of the slab 102 may be microscopic in nature. In someembodiments, the applied force can be present in the form of adifferential pressure across the slab 102. In some embodiments, anactuation element 110 may be in contact with the second surface 105 ofthe slab 102 to transfer a force to the slab 102. The actuation element110 can comprise a mechanical coupling between an exterior force and theslab 102. In some aspects, the actuation element 110 can comprise amechanical actuation element configured to transfer a force to the slab102. In some embodiments, the actuation element 110 may include aspherical object (such as the sphere shown in FIG. 1), a pin, anextender, a button, any other activation device, and/or a combinationthereof. It may be appreciated that other types of actuators may beutilized, such as, for example, slidable mounted plungers or shafts,point of contact type components other than spherical objects, and/or“T”-shaped transfer mechanisms, in accordance with alternativeembodiments. If desired, only a portion of an outer surface of theactuation element 110 may be spherical in shape or take on a particularshape. The actuation element 110 may be made of any material. Forexample, the actuation element 110 may be formed from stainless steel, apolymer, a ceramic, jeweled, another suitable metal, and/or anothersuitable material. In some cases, the actuation element 110 may includea stainless steel ball bearing. It is contemplated, however, that othergenerally spherical and other shaped elements may be used as or as partof the actuation element 110, if desired, including polymer basedobjects.

The deflection resulting from a force applied on the diaphragm throughan applied pressure and/or through the actuation element 110 maygenerally result in the deflection of the slab 102. The slab 102 may beconfigured to detect a deflection that is predominantly in a directionperpendicular to the plane of the slab 102. In this sense, the sense die100 is configured to measure a uniaxial force that is provided normal tothe plane of sense die 100.

The sense die 100 may have one or more sensing elements 120 and 124disposed on or adjacent to the slab 102, such as piezoresistive sensingelements or components formed using suitable fabrication or printingtechniques. For example, starting with the silicon sense die 100,standard pattern, implant, diffusion, and/or metal interconnectprocesses may be used to form one or more elements 120 and 124 on asurface 103, 105 of the sense die 100. For example, one or morepiezoresistive sense elements 120 and 124 may be formed on the slab 102.The piezoresistive sense elements 120 and 124 may be configured to havean electrical resistance that varies according to an applied mechanicalstress (e.g. deflection of the slab 102). The piezoresistive elements120 and 124 can thus be used to convert the applied force or pressureinto an electrical signal. In some instances, the piezoresistivecomponents may include a silicon piezoresistive material; however, othernon-silicon materials may be used.

One or more bond pads 130 and 134 may be formed on the upper surface 105of the sense die 100 and adjacent to the slab 102. Metal, diffusion, orother interconnects may be provided to interconnect the one or morepiezoresistive sensor elements 120 and 124 and the one or more bond pads130 and 134. As shown in FIG. 1, one or more of the piezoresistivesensor elements 120 and 124 can be electrically coupled to one or moreof the bond pads 130 and 134.

In some embodiments, the sense elements 120 and 124 may comprise aplurality of sense elements, for example two sense elements, three senseelements, four sense elements, or more. Similarly, the bond pads 130 and134 may comprise a plurality of bond pads, for example two bond pads,three bond pads, four bond pads, or more. FIG. 1 indicates typicallocations for the piezoresistive elements 120 and 124. These locationsmay be selected to be within an area of the slab 102, where the slab 102experiences forces from the contact with the actuation element 110.

Embodiments of the disclosure describe a sense die 100 where thepiezoresistive elements are located much closer to the contact areabetween the actuation element 110 and the slab 102 (or diaphragm), thana typical sense die.

FIGS. 2A-2C illustrate cross-sectional views of an actuation element 210(which may comprise a ball bearing) and a slab 202 of a sense die 200.The actuation element 210 may comprise a spheroid shape. The actuationelement 210 may contact and apply pressure to a contact area 220 betweenthe actuation element 210 and the slab 202. The slab 202 may comprise afirst surface 203, which may be attached to a structural frame 204. Theslab 202 may comprise a second surface 205 configured to contact theactuation element 210.

In some embodiments, the actuation element 210 may comprise stainlesssteel. In some embodiments, the actuation element 210 may compriseglass, sapphire, or another similar material. In some embodiments, thetotal length of the sense die 200 may be reduced by approximately 20% to30% compared to a typical sense die 200.

FIG. 2A illustrates a sense die 200 comprising a slab 202 attached to asubstrate 240 via an adhesive layer 242. The slab 202 may comprise senseelements 250 located on the surface 205 of the slab 202. The distancebetween the sense elements 250 is indicated by distance 260. The widthof the slab 202 is indicated by width 262.

In the embodiment shown in FIG. 2B, the slab 202 may comprise an etchedcavity 230 on the first surface 203 of the slab 202. However, in otherembodiments, such as FIGS. 2A and 2C, the slab 202 may not be etched. Inother words, the slab 202 may not comprise any thinned areas or cavitieson either surface 203 and 205 of the slab 202.

FIG. 2C illustrates a double cross-section of the slab 202, illustratinga quarter view of the slab 202 and actuation element 210. The slab 202may comprise four sense element 250 located about the contact point 220between the slab 202 and the actuation element 210.

In some embodiments, the sense elements 250 may be closer together thanin a typical sense die. In some embodiments, the distance 260 betweenthe sense elements 250 may be centered on the contact point 220 betweenthe actuation element 210 and the slab 202.

Referring to FIG. 2A, in some embodiments, the ratio between the width262 of the slab 202 and the distance 260 between the sense elements 250may be greater than approximately 3/1. In some embodiments, the ratiobetween the width 262 of the slab 202 and the distance 260 between thesense elements 250 may be greater than approximately 5/1. In someembodiments, the ratio between the width 262 of the slab 202 and thedistance 260 between the sense elements 250 may be greater thanapproximately 7/1. In some embodiments, the ratio between the width 262of the slab 202 and the distance 260 between the sense elements 250 maybe greater than approximately 11/1. In some embodiments, the ratiobetween the width 262 of the slab 202 and the distance 260 between thesense elements 250 may be less than approximately 20/1. In someembodiments, the sense elements 250 may not touch one another.

In some embodiments, the location of the sense elements 250 may bechosen based on the anticipated stress at a particular location on thesurface 205 of the slab 202.

Referring to FIGS. 3A-3C, a stress map 300 is shown illustrating thestress fields resulting from a force applied to the second surface 205of the slab 202 by the actuation element 210. The slab 202 and actuationelement 210 are shown above. The stress map 300 may comprise a plot ofthe difference between stress in the x direction (Sx) and stress in they direction (Sy) or Sx−Sy. The largest values, both positive andnegative, may indicate the locations on the surface 205 of the slabwhere the stress is the highest in one direction. These areas may becalled “hotspots” or high stress areas. The stress field generated onthe surface 205 at the hotspots 302 and 304 may be significantly greaterthan the stress field generated at other areas of the surface 205. Thehotspots 302 and 304 may create an ideal location for a piezoresistiveelement to be placed on the surface 205, where the piezoresistiveelement may detect the stress created at that location. The hotspots 302and 304 may be located closer to the contact area 220 than typicallocations for piezoresistive elements.

The stress map 300 shown in FIGS. 3A-3B may be cross-sectioned to show aquarter of the total surface 205 of the slab 202, wherein the corner 310illustrates the center of the contact area 220 (as shown above) betweenthe actuation element and the slab. Referring to FIG. 3C, a full stressmap 300 may comprise up to four hotspots 302, 304, 306, and 308surrounding the center 310 of the contact area 220 between the actuationelement and the slab. The typical locations for piezoresistive elementsare indicated by “x” 322, 324, 326, and 328.

Using the information from the stress map 300 shown in FIGS. 3A-3C, thepiezoresistive elements (such as 120 and 124 described above) may beplaced within one of the hotspots 302, 304, 306, and 308 indicated bythe stress map 300. While the stress at the typical locations 322, 324,326, and 328 for the piezoresistive elements may be within an area thatwill detect stress on the slab surface 205, the hotspots 302, 304, 306,and 308 may produce significantly higher outputs, thereby improving theaccuracy and sensitivity of the piezoresistive elements. For example,Sx−Sy stress at the typical locations 322, 324, 326, and 328 forpiezoresistive elements may be approximately ±70 megapascal (MPa), andstress in the hotspots 302, 304, 306, and 308 may be approximately ±1400MPa (approximately 20 times higher than the typical stress readings).The increased stress reading may produce an increased signal output forthe piezoresistive elements.

Unlike a typical pressure sensor comprising an anisotropic etch, theSx−Sy stress peak measured on the surface 205 of the slab moves outwardradially from the contact area 220 as the load on the surface 205 isincreased. In other words, the hotspots may change in location based onthe magnitude of the force applied to the slab via the actuationelement. For example, the distance from the center 310 at which thehotspot occurs may increase as the magnitude of the force increases.This concept may be illustrated by the following graphs and figures.

Piezoresistive elements located at different positions with respect tothe center of the surface 205 were evaluated at a range of forcesapplied to the surface 205. The results are show in the graphs of FIGS.4A-4B. As an example, the locations ranged from approximately 39 microns(μm) from the center to approximately 310 μm from the center.

Referring to FIG. 4A, the sensor output in millivolts (mV) is plottedagainst the load applied to the slab in Newtons (N). Each line indicatesa different location for the piezoresistive elements, measured inradians from the center of the contact area between the slab and theactuation element. The traditional location of the piezoresistiveelements is also plotted, for reference, wherein the distance from thecenter is higher in a traditional sensor. For each line on the graph,the sensor output builds as the load increases until the Sx−Sy peakpasses through the location of the piezoresistive element, and then thenthe output drops off. Sensor function may be optimal before the peak inthe lines.

Referring to FIG. 4B, the graph illustrates the results show in FIG. 4Athat have been normalized using a standard of the traditional sensorlocation output (at a distance of 890 μm), where the results for each ofthe locations have been divided by the standard. The graph shown in FIG.4B illustrates that the sensor output may be relatively constant beforethe peak (for that location), and may be usable for determining stresson the slab at that location.

For most sensor applications, it may be possible to estimate the rangeof the load expected for a particular application. Using the graphs andthe estimated load (in N), an optimal location for the piezoresistiveelements may be chosen. For example, if the expected load is less than 5N, the location for the piezoresistive elements may be chosen to be at adistance of between approximately 30 to 80 μm from the center. Asanother example, if the expected load is between 10 and 20 N, thelocation for the piezoresistive elements may be chosen to be at adistance of between approximately 100 to 120 μm from the center.

Referring to FIG. 5, an additional graph illustrates the approximaterelationship between the contact radius between the flat surface of theslab and the curved surface of the spherical actuation element, and theestimated load that will be applied to the sense die. As the loadincreases, what is initially a point contact between the slab and theactuation element, widens out into circular contact. FIG. 5 is a plot ofthe radius of that circle of contact vs. force applied by the actuationelement. In some embodiments, it may be desirable to locate the senseelements outside the contact radius, to avoid contact between theactuation element and the sense elements. However, in some embodiments,the actuation element may contact one or more of the sense elementsduring the use life of the sense die.

To further evaluate the effect of locating the piezoresistive elementscloser to the center of a slab, sense die were analyzed to solve for thegenerated signal. At approximately 1 N force applied to the slab, thesignal from a piezoresistive element located at the typical location of890 μm from the center may produce approximately 3.6 mV. When thelocation of the piezoresistive element was changed to 310 μm from thecenter, the signal may rise to approximately 27.3 mV (approximately 7.6times the typical output). When the location of the piezoresistiveelement was changed to 150 μm from the center, the signal may rise toapproximately 87.2 mV (approximately 246 times the typical output).

Additionally, it may be desirable to provide accurate measurements forforces lower than 1 N. Force detection in this low range may typicallybe difficult to achieve with adequate over-load protection. To furtherevaluate the effect of locating the piezoresistive elements closer tothe center of a slab, sense dies were tested to determine the generatedsignal in force ranges of approximately 1 N (100 g), approximately 0.1 N(10 g), approximately 0.01 N, and approximately 0.001 N.

As described above, the closer a piezoresistive element is location tothe center (i.e. the smaller the distance from the center), the higherthe sensitivity of the output signal. In the following results, theclosest location for the piezoresistive element was approximately 150 μmfrom the center. For a force range of 0.1 N, at a location of 150 μmfrom the center, the sensor output may be approximately 8.8 mV.

As the force ranges decrease below 1 N, it may be proportionally harderto develop sufficient output signal. Therefore, the use ofpiezoresistive elements positioned closer to the center of the slab mayallow for improved signal output for lower force ranges.

FIGS. 6A-6B further illustrate the relationship between the contactradius, i.e. the distance from the center 310 of the slab 202 at whichthe piezoresistive element is located, and the estimated load that willbe applied to the sense die. In FIG. 6A, the force applied to theactuation element 210 is approximately 25 N. The contact radius to thefirst hotspot 302 is indicated by distance 602. Similarly, the contactradius to the second hotspot 304 is indicated by distance 604.

In FIG. 6B, the force applied to the actuation element 210 is increasedto approximately 100 N. The distance 602 to the first hotspot 302 hasincreased accordingly. Similarly, the distance 604 to the second hotspot304 has increased accordingly. Therefore, the optimal location for thepiezoresistive elements to be located at or near a hotspot 302 and 304depends on the amount of force that is anticipated to be applied to theslab 202.

The sensitivity (measured in mV/V) of the sense elements described abovewas determined via modeling, and then compared to a standard or typicalsensor. The different locations of the sense elements were compared toone another as well. In some embodiments, the sensitivity ratio (whencompared to a typical sensor) may be greater than approximately 1/1. Insome embodiments, the sensitivity ratio may be greater thanapproximately 5/1. In some embodiments, the sensitivity ratio may begreater than approximately 10/1. In some embodiments, the sensitivityratio may be greater than approximately 20/1. In some embodiments, thesensitivity ratio may be greater than approximately 25/1.

In a first embodiment, a sense die may comprise a chip comprising aslab; one or more sense elements supported by the slab, wherein theratio of the width of the slab to the distance between the one or moresense elements is at least 2/1; one or more bond pads supported by afirst side of the chip, each of the one or more bond pads electricallycoupled to at least one of the one or more sense elements; a structuralframe disposed on the first side of the chip, wherein the structuralframe is disposed at least partially about the slab; and one or moreelectrical contacts extending through the structural frame, wherein theone or more electrical contacts are electrically coupled to the one ormore bond pads.

A second embodiment can include the sense die of the first embodiment,wherein the sense elements comprise piezoresistive elements.

A third embodiment can include the sense die of the first or secondembodiments, further comprising an actuation element configured tocontact the slab at or near the center of the slab.

A fourth embodiment can include the sense die of the third embodiment,wherein the distance between the sense elements is centered on thecontact point between the slab and the actuation element.

A fifth embodiment can include the sense die of any of the first tofourth embodiments, wherein the ratio of the width of the slab to thedistance between the one or more sense elements is greater thanapproximately 5/1.

A sixth embodiment can include the sense die of any of the first tofifth embodiments, the ratio of the width of the slab to the distancebetween the one or more sense elements is greater than approximately10/1.

A seventh embodiment can include the sense die of any of the first tosixth embodiments, wherein the locations of the one or more senseelements are determined by mapping the force on the slab applied by theactuation element, and identifying one or more hotspots on the slabwhere the force is higher than the surrounding areas.

An eighth embodiment can include the sense die of any of the first toseventh embodiments, wherein the locations of the one or more senseelements are determined by determining a correlation between theestimated force that will be applied to the slab and the desiredlocation for sense elements on the slab.

In a ninth embodiment, a method of sensing a force using a sense die maycomprise providing a sense die comprising a chip having a slab formedthereon; applying a force to the slab of the sense die; and determiningthe magnitude of the force applied to the slab via one or more senseelements attached to the slab, wherein the ratio of the width of theslab to the distance between the one or more sense elements is greaterthan approximately 2/1.

A tenth embodiment can include the method of the ninth embodiment,further comprising determining a correlation between the estimated forcethat will be applied to the slab and the desired location for senseelements on the slab.

An eleventh embodiment can include the method of the tenth embodiment,wherein as the estimated force increases, the desired location for thesense elements increases in distance from the center of the slab.

A twelfth embodiment can include the method in of any of the ninth toeleventh embodiments, wherein applying a force comprises contacting theslab with an actuation element.

A thirteenth embodiment can include the method of the twelfthembodiment, wherein the distance between the sense elements is centeredon the contact point between the slab and the actuation element.

A fourteenth embodiment can include the method of any of the ninth tothirteenth embodiments, wherein the ratio of the width of the slab tothe distance between the one or more sense elements is greater thanapproximately 5/1.

A fifteenth embodiment can include the method of the any of the ninth tofourteenth embodiments, further comprising mapping the force on the slabapplied by the actuation element; identifying one or more hotspots onthe slab where the force is higher than the surrounding areas; anddetermining the location for a piezoresistive element to be located onthe slab based on the location of the hotspots.

In a sixteenth embodiment, a sense die may comprise a chip comprising aslab; an actuation element configured to contact the slab at or near thecenter of the slab, and configured to apply a force to the slab; and oneor more sense elements supported by the slab, wherein the ratio of thewidth of the slab to the distance between the one or more sense elementsis greater than approximately 2/1, and wherein the distance between thesense elements is centered on the contact point between the actuationelement and the slab.

A seventeenth embodiment can include the sense die of the sixteenthembodiment, wherein the sense elements comprise piezoresistive elements.

An eighteenth embodiment can include the sense die of the sixteenth orseventeenth embodiments, wherein the ratio of the width of the slab tothe distance between the one or more sense elements is greater thanapproximately 5/1.

A nineteenth embodiment can include the sense die of any of thesixteenth to eighteenth embodiments, wherein the ratio of the width ofthe slab to the distance between the one or more sense elements is lessthan approximately 20/1.

A twentieth embodiment can include the sense die of any of the sixteenthto nineteenth embodiments, wherein the sense elements are located at ornear hotspots identified on the surface of the slab by force mapping.

While various embodiments in accordance with the principles disclosedherein have been shown and described above, modifications thereof may bemade by one skilled in the art without departing from the spirit and theteachings of the disclosure. The embodiments described herein arerepresentative only and are not intended to be limiting. Manyvariations, combinations, and modifications are possible and are withinthe scope of the disclosure. Alternative embodiments that result fromcombining, integrating, and/or omitting features of the embodiment(s)are also within the scope of the disclosure. Accordingly, the scope ofprotection is not limited by the description set out above, but isdefined by the claims which follow, that scope including all equivalentsof the subject matter of the claims. Each and every claim isincorporated as further disclosure into the specification and the claimsare embodiment(s) of the present invention(s). Furthermore, anyadvantages and features described above may relate to specificembodiments, but shall not limit the application of such issued claimsto processes and structures accomplishing any or all of the aboveadvantages or having any or all of the above features.

Additionally, the section headings used herein are provided forconsistency with the suggestions under 37 C.F.R. 1.77 or to otherwiseprovide organizational cues. These headings shall not limit orcharacterize the invention(s) set out in any claims that may issue fromthis disclosure. Specifically and by way of example, although theheadings might refer to a “Field,” the claims should not be limited bythe language chosen under this heading to describe the so-called field.Further, a description of a technology in the “Background” is not to beconstrued as an admission that certain technology is prior art to anyinvention(s) in this disclosure. Neither is the “Summary” to beconsidered as a limiting characterization of the invention(s) set forthin issued claims. Furthermore, any reference in this disclosure to“invention” in the singular should not be used to argue that there isonly a single point of novelty in this disclosure. Multiple inventionsmay be set forth according to the limitations of the multiple claimsissuing from this disclosure, and such claims accordingly define theinvention(s), and their equivalents, that are protected thereby. In allinstances, the scope of the claims shall be considered on their ownmerits in light of this disclosure, but should not be constrained by theheadings set forth herein.

Use of broader terms such as “comprises,” “includes,” and “having”should be understood to provide support for narrower terms such as“consisting of,” “consisting essentially of,” and “comprisedsubstantially of.” Use of the terms “optionally,” “may,” “might,”“possibly,” and the like with respect to any element of an embodimentmeans that the element is not required, or alternatively, the element isrequired, both alternatives being within the scope of the embodiment(s).Also, references to examples are merely provided for illustrativepurposes, and are not intended to be exclusive.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods may beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted or not implemented.

Also, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as directly coupled or communicating witheach other may be indirectly coupled or communicating through someinterface, device, or intermediate component, whether electrically,mechanically, or otherwise. Other examples of changes, substitutions,and alterations are ascertainable by one skilled in the art and could bemade without departing from the spirit and scope disclosed herein.

What is claimed is:
 1. A sense die comprising: a chip comprising a slab;one or more sense elements supported by the slab, wherein the ratio ofthe width of the slab to the distance between the one or more senseelements is at least approximately 2/1; one or more bond pads supportedby a first side of the chip, each of the one or more bond padselectrically coupled to at least one of the one or more sense elements;a structural frame disposed on the first side of the chip, wherein thestructural frame is disposed at least partially about the slab; and oneor more electrical contacts extending through the structural frame,wherein the one or more electrical contacts are electrically coupled tothe one or more bond pads.
 2. The sense die of claim 1, wherein thesense elements comprise piezoresistive elements.
 3. The sense die ofclaim 1, further comprising an actuation element configured to contactthe slab at or near the center of the slab.
 4. The sense die of claim 3,wherein the distance between the sense elements is centered on thecontact point between the slab and the actuation element.
 5. The sensedie of claim 1, wherein the ratio of the width of the slab to thedistance between the one or more sense elements is greater thanapproximately 5/1.
 6. The sense die of claim 1, wherein the ratio of thewidth of the slab to the distance between the one or more sense elementsis greater than approximately 10/1.
 7. The sense die of claim 1, whereinthe locations of the one or more sense elements are determined bymapping the force on the slab applied by the actuation element, andidentifying one or more hotspots on the slab where the force is higherthan the surrounding areas.
 8. The sense die of claim 1, wherein thelocations of the one or more sense elements are determined bydetermining a correlation between the estimated force that will beapplied to the slab and the desired location for sense elements on theslab.
 9. A method of sensing a force using a sense die, the methodcomprising: providing a sense die comprising a chip having a slab formedthereon; applying a force to the slab of the sense die; and determiningthe magnitude of the force applied to the slab via one or more senseelements attached to the slab, wherein the ratio of the width of theslab to the distance between the one or more sense elements is greaterthan approximately 2/1.
 10. The method of claim 9, further comprisingdetermining a correlation between the estimated force that will beapplied to the slab and the desired location for sense elements on theslab.
 11. The method of claim 10, wherein as the estimated forceincreases, the desired location for the sense elements increases indistance from the center of the slab.
 12. The method of claim 9, whereinapplying a force comprises contacting the slab with an actuationelement.
 13. The method of claim 12, wherein the distance between thesense elements is centered on the contact point between the slab and theactuation element.
 14. The method of claim 9, wherein the ratio of thewidth of the slab to the distance between the one or more sense elementsis greater than approximately 5/1.
 15. The method of claim 9, furthercomprising: mapping the force on the slab applied by the actuationelement; identifying one or more hotspots on the slab where the force ishigher than the surrounding areas; and determining the location for apiezoresistive element to be located on the slab based on the locationof the hotspots.
 16. A sense die comprising: a chip comprising a slab;an actuation element configured to contact the slab at or near thecenter of the slab, and configured to apply a force to the slab; and oneor more sense elements supported by the slab, wherein the ratio of thewidth of the slab to the distance between the one or more sense elementsis greater than approximately 2/1, and wherein the distance between thesense elements is centered on the contact point between the actuationelement and the slab.
 17. The sense die of claim 16, wherein the senseelements comprise piezoresistive elements.
 18. The sense die of claim16, wherein the ratio of the width of the slab to the distance betweenthe one or more sense elements is greater than approximately 5/1. 19.The sense die of claim 16, wherein the ratio of the width of the slab tothe distance between the one or more sense elements is less thanapproximately 20/1.
 20. The sense die of claim 16, wherein the senseelements are located at or near hotspots identified on the surface ofthe slab by force mapping.